SAF-TE

In computer storage, SAF-TE (abbreviated from SCSI Accessed Fault-Tolerant Enclosure) is an industry standard to interface an enclosure to a (parallel) SCSI subsystem to gain access to information or control for various elements and parameters. These include temperature, fan status, slot status (populated/empty), door status, power supplies, alarms, and indicators (e.g. LEDs, LCDs).[1] Practically, any given SAF-TE device will only support a subset of all possible sensors or controls.[2]

Scope

A SCSI backplane with SCA-2 connectors inside an enclosure (SAF-TE device not visible)

Many RAID controllers can utilize a SAF-TE "activated" backplane by detecting a swapped drive (after a defect) and automatically starting a rebuild. A passive subsystem usually requires a manual rescan and rebuild.

A SAF-TE device (SEP) is represented as a SCSI processor device that is polled every few seconds by e.g. the RAID controller software.[1] Due to the low overhead required, impact on bus performance is negligible.[3] For SAS or Fibre Channel systems, SAF-TE is replaced by the more standardized SCSI Enclosure Services (SES).

The most widely used version was defined in the SAF-TE Interface Specification Intermediate Review R041497, released on April 14, 1997 by nStor (now part of Seagate Technology) and Intel.

Command interface

Status requests are performed as READ BUFFER SCSI commands, enclosure action requests as WRITE BUFFER commands.[2]

Command typeOpcodemandatory / optionalCommandDescription
READ BUFFER 00hmRead enclosure configurationinquire about system components in the enclosure
01hmRead enclosure statusinquire about operational status of enclosure components
02hoRead usage statisticsfetch information about total usage time and number of power-cycles
03hoRead device insertionsreturns information on how many times a device has been inserted into each enclosure slot
04hmRead device slot statusreturns information on the current state of each slot
05hoRead global flagsread global flags from processor
WRITE BUFFER 10hmWrite device slot statusupdates state of the slots, essentially drives LEDs, alarms etc.
11hoSet SCSI IDset the SCSI ID of any device on the channel
12hmPerform slot operationprepare a slot for insertion or removal (electronically or mechanically)
13hoSet fan speedset rotational speed for each fan
14hoActivate power supplyturn a power supply on or off
15hmSend global flagssend global flags to processor (audible alarm; indicators for global failure, global warning, enclosure power, fan/cooling failure, power failure, drive failure, drive warning, array failure, array warning; enclosure lock; enclosure identification)

See also

References

  1. SAF-TE IR 1.0 Introduction
  2. SAF-TE IR 3.0 SAF-TE Interface
  3. SAF-TE IR 2.0 SCSI Specification
  • www.safte.org
  • SAF-TE as part of Intel's IPMI
  • SAF-TE Intermediate Review R041497
  • Alexander Motin (September 22, 2011). "Enclosure Management in FreeBSD" (PDF).


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